The present invention is directed to an improved network control system and method for use in a communication network of the type including a plurality of nodes coupled to a bidirectional bus. The network control system and method is arranged to control the receipt and transmission of messages and provide control and supervisory functions at one of the network nodes. In a preferred network, each node is associated with a network control system of the present invention which correspondingly implements the method of the present invention.
Communication networks find application in virtually every environment wherein information is conveyed from one point to another. There are essentially two types of communication networks, connection-oriented networks and connectionless networks. In connection-oriented networks, a connection is established between like protocol stages of the network from the originating point of a message to the destination point of the message. A telecommunications network is one example of a connection-oriented network. A connectionless network, in contrast, is a network wherein there is no prior coordination between any of the like protocol stages from the origination point of a message to the destination point of the message. In addition, in a connectionless network, each message is transmitted independently of the previously or subsequently transmitted messages.
Connection-oriented networks are best suited for applications wherein a large amount of information is conveyed at any one time and wherein there are minimal time constraints on the system. This is due to the fact that the establishment of each connection between like protocol stages of the network requires considerable connection reliability and the establishment of all the required connections across the network consumes considerable time. Hence, a large amount of overhead is required in connection-oriented networks for conveying a message from one point to another. This is justified when a large amount of information is conveyed at any one time.
While there are many applications for communication networks, such networks have not been utilized in the field of controls, and more particularly, in facility management systems. Such systems are employed in office buildings, manufacturing facilities, and the like, for controlling the internal environment of the facility and/or for monitoring security systems such as fire and burglar alarms. These systems, have been arranged in master-slave configuration for acting, on a real-time basis, on security system alarms and controlling field devices such as heaters, dampers, fans and the like. Hence, these systems have not required communication networks to provide their required function.
A now and improved facility management system has been recently developed which has taken a clear departure from the master-slave configurations of the past. This new system is distributed in configuration, but still must function on a real-time basin. This requires short messages to be convoyed within the system and under certain time constraint. Because this system is distributed in configuration, it requires a communication network unlike prior master-slave systems.
Although traditional connection-oriented networks are more common, they are not well-suited for such an application. Because this system is a distributed system, many connections would have to be established to convey a message from one point of the system to another point in the system. Since the messages within this facility management system are generally short, due to the required real-time operation, the overhead associated with establishing the required connections would not be justified.
There is, therefore, a need in the art for a connectionless network control system which is distributed in its architecture to correspond to the distributed configuration of a control system, such as a facility management system. The present invention provides such a network control system and method which is distributed in architecture and which provides high reliability. The present invention further provides such a network control system which includes a connection-oriented network control portion for use in controlling the transmission and receipt of messages containing a large amount of information between one point in the network and another.
It is therefore a general object of the present invention to provide a connectionless network control system and method for use in a communication network.
It is a further object of the present invention to provide a connectionless network control system and method for use in a communication network which exhibits high reliability.
It is a further object of the present invention to provide such a connectionless network control system and method which may be utilized in a facility management system.
It is a still further object of the present invention to provide a network control system which includes a connectionless network control portion for controlling the receipt and transmission of short messages combined with a connection-oriented network control portion for controlling the transmission and receipt of long messages.